One image processing method at an edge portion of an image is disclosed in, for example, Japanese Patent Kokai (Laid-Open) Publication No. 2002-16820. In this image processing method, absolute values of derivatives of an input image signal are calculated, an average of the absolute values is calculated, subtractions between the calculated absolute values and the calculated average are calculated, and a scaling ratio of the input image signal is controlled in accordance with the subtractions.
Further, another image processing method at an edge portion of an image is disclosed in, for example, Japanese Patent Kokai (Laid-Open) Publication No. 2000-101870. In this image processing method, a control signal is generated from a high-frequency component of an input image signal, and a phase of an interpolation pixel is controlled by the control signal.
However, the conventional image processing methods described above improve sharpness of an edge portion in accordance with an amount of the high-frequency component of the input image signal, so that there is a problem that sharpness of an edge portion with a small change in a level of the image signal is less improved than sharpness of an edge portion with a great change in a level of the image signal. Therefore, it was difficult to improve sharpness of the entire image in proper quantities.
Accordingly, an object of the present invention is to provide an image processing apparatus, an image display apparatus, an image processing method, and an image display method, which can properly improve sharpness of an edge portion of an image.